Aqueous coating compositions are known and described for example in U.S. Pat. Nos. 4,794,147; 4,791,168; 4,518,724; and 4,403,055.
These aqueous coating compositions comprise a principal resin, and may contain a crosslinker, pigments dispersed in a grind resin and other additives such as solvents, control agents, fillers and the like.
Many pigments, especially organics, used in coating compositions for the automotive industry are hydrophobic. These pigments, when used in aqueous coating systems require the use of specialized grind resins with the additions of dispersing agents and solvents to overcome their incompatibility with water and poor ability to grind.
Pigment pastes are usually prepared by dispersing a pigment in a grind resin in the presence of plasticizers, wetting agents, surfactants or other ingredients in a ball mill, sand mill or continuous mill, until the pigment has been reduced to the desired particle size and is wetted by the resin or dispersed in it.
One disadvantage of pigment pastes is that the pastes often require a large amount of resin relative to pigment, and the resulting pigment pastes are not very concentrated. In addition, pastes made with conventional resins often do not have optimum color development.
The present invention is directed to a pigment dispersant for an aqueous coating composition that provides stable aqueous pigment pastes or pigment dispersions. The dispersants of the present invention provide pigment grinds with enhanced formulating latitude. The present invention is also directed to an aqueous coating composition containing the pigment dispersants and an article coated with the coating composition.